Centrifugal pumps are in their usual design not self-drawing, which means they are not capable to evacuate even only relatively short suction pipes and to pass over into a normal pump operation after moving the air which is in the suction pipe away.
The self-drawing capability and thus the capability to move a limited amount of air is of importance for all those cases in which it is not possible to provide a check valve, for example a foot valve, in the suction pipe, where same, for example caused by contamination of the liquid, does not reliably seal.
In order to make a normal centrifugal pump self-drawing, various measures are known, which are divided basically into measures on the rotor, for example:
Mounting of an auxiliary rotor on the back side of the rotor with connecting channels to the main rotor or
Construction of the rotor with at least one channel constriction in order to achieve a turbulence,
AND INTO MEASURES ON THE STATIONARY PUMP PART, FOR EXAMPLE
Construction of the spiral housing with a drawing pipe on the housing projection (see for example Austrian Pat. No. 272,848),
Arrangement of a by-pass from the pressure to the suction side (with or without lock after the end of evacuation) and asymmetric construction of the distributor with an inflow or recirculation opening.
These known measures are disadvantageous in as far as they either, during the phase of the movement of the liquid, very strongly reduce the efficiency or require additional structural measures on the pump housing, which on the one hand substantially increases the manufacturing price and on the other hand make the pump substantially larger.
For example the known construction with the asymmetrical distributor, on which the present invention is based, requires special measures on the pressure side, for example a pressure tight water box, so that the liquid gas mixture can calm down and the escape of gas from the liquid is made possible.
Aside from the expenses of this construction there are cases of use where such enlarged pressure chambers cannot be used for reasons of available space or because of the outer shape.
Thus the basic purpose of the invention is to provide a centrifugal pump of the above described type in which these disadvantages are voided. This is inventively achieved by arranging flaps or the like in the channels of the distributor, through which flaps the channels can be closed off or blocked during the suction phase.
The blades of the distributor are preferably constructed with recesses for receiving the flaps. The flaps may be either spring-loaded or resilient.
Since in this pump the liquid gas mixture leaves the distributor without any substantial speed, the gas, in particular the air, which is contained in it, can be given out easier. The air cannot return into the rotor space, but rises and is moved away through the pressure port, however, the degassed liquid returns through at least one inflow or recirculation opening which is arranged preferably far down into the rotor space where it again is mixed with air and is moved away with same until the suction pipe is completely evacuated.
After the evacuation is completed, full conveying starts and the flaps in the channels open up according to the increasing conveyed stream until the cross section is fully utilized. The small throttle effect caused by the counterspringiness of the flaps is of no importance during the strong flow during the normal liquid conveyance of the pump. Also the loss in efficiency caused by the constant backflow through the inflow or recirculation opening can be absorbed easily, if same is arranged on the side of the pump which lies opposite to the pressure port.